I have three Linux servers in Digital Ocean; all three servers have ports TCP and UDP 53 open to the public through DigitalOcean firewall, everything is fine this point. both centos servers are running NxFilter for DNS filtering and both are working 100%. we have 5 offices around the city that use those centos servers as their DNS servers for web content filter; at this point, everything is working as supposed to be, everybody is happy.
I want to use the Ubuntu server as a switch to alternate between the two centos servers; I mean.. this week will be using centos server #1 for web content filter, but next week we want to use centos server #2, so the computers in the offices will be using the ubuntu server as their DNS server.
I tried to use the floating IP address service from Digital Ocean, but this service doesn't support UDP traffic.
I tried to apply some iptables rules on ubuntu server with partial success because I was able to redirect UDP/53 traffic to centos server #1, but centos server #1 sees the traffic coming from ubuntu server, not from the office's public IP address, and NxFilter applies the web filter based on the source IP address.
About the recuiterMember since Mar 14, 2020 Tirlok Singh
from Yucatan, Mexico